Field of the Invention
The present invention relates to a radiation imaging system which obtains a radiation image of an object by irradiating it with radiation, a control apparatus, a radiation imaging apparatus and a control method.
Description of the Related Art
Recently, a radiation imaging system has been used in various fields, and has become an important means for diagnosis especially in the medical field. A radiation imaging system in the medical field is configured to irradiate, from an irradiating unit, an object with the radiation generated by a radiation generating apparatus and obtain a radiation image by sensing the radiation transmitted through the object using a radiation imaging apparatus. The control apparatus of the radiation imaging system performs image processing for the radiation image obtained in this manner and displays the resultant image on, for example, a monitor, thereby making the radiation image useful for diagnosis.
The above radiation imaging system sometimes uses a packet communication network for the transfer of a radiation image from the radiation imaging apparatus to the control apparatus in order to promote downsizing and generalization of transmission lines, wireless communication, and the like. The above packet communication is the communication operation of dividing data into small units and transmitting/receiving the data units one by one. Each divided data described above is called a packet.
In order to reliably transmit data to the control apparatus by using a packet communication network, a protocol having a retransmission function such as TCP (Transmission Control Protocol) is generally used. However, when using TCP, it is difficult to increase a date rate for retransmission handling. TCP is one of the Internet standard protocols which form a reliable connection between processes of transmission and reception hosts and perform retransmission or the like at the occurrence of a data loss. This protocol is high in reliability but low in transmission efficiency. In addition, the protocol suffers large packet arrival delays and sometimes cannot meet the requirement to display in real time.
For this reason, UDP (User Datagram Protocol) is used to achieve a reduction in delay. However, UDP generates no connection and makes no acknowledgement. For this reason, this protocol has a risk of a packet loss even though it can perform high-speed transmission. UDP is a connectionless communication designed only for the transmission/reception of data between applications, and is one of the Internet standard protocols which entrust reliability to applications. This protocol is low in reliability but high in transmission efficiency.
As described above, when a packet is lost at the time of transmission/reception of data by using UDP communication, the data transferred from the transmission side sometimes does not normally arrive at the reception side. That is, when a packet loss occurs in a radiation imaging system, the radiation image transmitted from the radiation imaging apparatus does not normally arrive at the control apparatus. A study has been made on a technique of retransmitting packet data on the UDP layer as a method of solving this problem. This method is disclosed in Japanese Patent Laid-Open Nos. 2010-088027 and 2013-180134.
However, the packet loss is not the only cause of the situation in which the radiation image transmitted from the radiation imaging apparatus does not normally arrive at the control apparatus. For example, when an abnormality occurs on the control apparatus side or unintentional power discontinuity occurs during the transmission of a radiation image from the radiation imaging apparatus to the control apparatus, the control apparatus side may not receive the radiation image transmitted from the radiation imaging apparatus. When such a situation occurs, even if an object is irradiated with radiation, the radiation image does not arrive at the control apparatus. As a consequence, the radiation image is lost, and the object undergoes ineffective exposure. In addition, when the radiation image is lost, it is necessary to image the object again. That is, the operator needs to perform imaging all over again, resulting in an operation time loss.